Method and apparatus for reducing oscillatory camshaft torque in an internal combustion engine

ABSTRACT

A peristaltic piston pump driven by a dedicated pump cam disposed on a camshaft of an engine. A plurality of valve-opening cams are also disposed along the camshaft. The pump cam has a plurality of lobes equal in number to the number of valve cams and each pump lobe is disposed at 180° from a valve cam lobe such that the camshaft valve torque and secondary oil pump camshaft torque partially cancel, reducing overall camshaft torque oscillation. The pump includes a lost-motion shuttle and spring to permit continuous response of the pump to the cam.

TECHNICAL FIELD

The present invention relates to oil pumps for internal combustionengines; more particularly, to a secondary oil pump for boosting oilpressure when the output pressure of the primary engine oil pump is low;and most particularly, to a secondary oil pump driven by a cam on theengine's camshaft wherein pump-actuating cam lobes are out of phase withvalve actuating cam lobes.

BACKGROUND OF THE INVENTION

Oil pumps for internal combustion engines are well known. A primaryengine oil pump may be, for example, a mechanically-drivenpositive-displacement gear pump fed from the engine's crankcase anddriven by rotation of the engine's camshaft or crankshaft. Oil pumpoutput flow is typically a direct function of the rotary speed of theengine. Because of engineered oil leaks between lubricated components inthe oil pathway, and because of wear in those components during thelifetime of the engine, oil pressure also may be relatively low duringperiods of low engine speeds such as at idle and increases only asengine speed increases. Also, as engine temperature increases, oilviscosity decreases in known fashion, causing increased flow through theleaks and consequent reduced line pressure. In addition to insufficientengine lubrication, low oil pressure can result in slow or faultyactuation of oil-driven auxiliary engine devices, for example, camshaftphasers and variable valve actuators.

It is known to use an electrically-driven auxiliary pump to increase oilpressure for oil being supplied to a variable valve actuation mechanism.

What is needed is an inexpensive, reliable, mechanical means formaintaining a minimum oil pressure and flow in an internal combustionengine.

Another problem in an internal combustion engine is the amplitude oftorque oscillation of the engine's camshaft(s). During operation of theengine, while each valve is closed, the follower for the associated camrides on the base circle portion of the cam. To open the valve, thefollower rides up the front side of the eccentric lobe. The resistancecaused by the opposing force of the valve return spring places a torqueon the camshaft in a direction counter to the rotational direction ofthe camshaft. After the peak of the lobe is passed and the valve isclosing, the direction of torque is reversed as the follower rides downthe back side of the lobe, urged by the force of the valve spring. Thecamshaft is thus subjected to relatively violent torque reversals foreach engine valve actuation resulting in oil pressure fluctuation(especially within the camshaft phaser), undesirable vibration, wear,and energy loss in the form of heat.

What is needed is a means for reducing the amplitude of torqueoscillation of an engine camshaft.

It is a principal object of the present invention to reduce theamplitude of torque oscillation of an engine camshaft.

SUMMARY OF THE INVENTION

Briefly described, a secondary oil supply pump augments oil flow from aprimary supply pump in an internal combustion engine. The secondary pumpis a peristaltic piston pump driven by a dedicated cam disposed on acamshaft of the engine. Preferably, the pump cam is formed having aplurality of lobes equal in number to the number of valves actuated bythe camshaft, and further, that each pump cam lobe is disposed at 180°from a valve cam lobe such that the torque exerted by the closing valveassists in providing a pumping pulse to the secondary oil pump; and thetorque exerted by termination of the pumping pulse assists in openingthe next valve. In this way, the net amplitude of the camshaft torqueoscillation is substantially reduced. A three-way valve responsive toinline pressure and, preferably, an engine control module governs theflow of oil either around the secondary pump at acceptably high primarypump pressures or through the secondary pump when primary pressure isunacceptably low.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will now be described, by way of example, withreference to the accompanying drawings, in which:

FIG. 1 is a schematic diagram of an oil circulation system for aninternal combustion engine in accordance with the invention;

FIG. 2 is an elevational cross-sectional view of a secondary oil supplypump actuated by a camshaft cam in accordance with the invention,showing the pump on a base circle portion of the cam;

FIG. 3 is an elevational cross-sectional view like that shown in FIG. 2,showing the pump in cam-actuated mode;

FIG. 4 is an elevational cross-sectional view like that shown in FIGS. 2and 3, showing the pump in non-pumping lost-motion mode;

FIG. 5 is a graph of camshaft torque as a function of rotational angleof a camshaft for a three-cylinder application, showing a reduction incamshaft torque oscillation as a result of the invention; and

FIG. 6 is an view of a camshaft in accordance with one embodiment of theinvention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to FIG. 1, in a schematic diagram for an oil circulationsystem 10 for an internal combustion engine, an oil sump 12, such as anengine crankcase, supplies oil to a conventional primary oil pump 14.Pump 14 supplies oil under pressure to the rest of the system via athree-way valve 16 disposed at the exit of a secondary oil supply(booster) pump 18 in accordance with the invention. Oil from primarypump 14 may flow either around or through secondary pump 18 via lines19,20, as selected by valve 16 in accordance with conditions describedbelow.

Oil flows from valve 16 via line 21 to other lubricated elements, suchas a control valve 22 for controlling the action of camshaft phaser 24,a variable valve actuation mechanism 26, and general lubrication ofengine 28, via an optional oil accumulation reservoir 30. Alllubrication paths lead eventually back to sump 12.

Referring to FIG. 2, peristaltic secondary oil pump 18 includes a pumpbody 32 having a transverse bore 34 and a blind bore 36 orthogonal totransverse bore 34. Blind bore 36 preferably is provided with a ventopening 38. Within transverse bore 34 on opposite sides of blind bore 36are disposed first and second check valves 40,42 for permitting oil flowonly in the direction from line 20 to line 21 and not the reverse. Alost-motion shuttle 44 having a length shorter than the depth of blindbore 36 is slidingly disposed in blind bore 36 and is captured thereinby plate 46. A lost-motion spring 48 is disposed in compression in asecond well 50 in shuttle 44 to bias shuttle 44 toward plate 46. A camfollower 52 is slidingly disposed in a first well 54 in shuttle 44 andextends through an opening in plate 46 for engaging a cam 56 fixedlydisposed on a camshaft 58 of engine 28. Of course, cam follower 52 maybe a roller follower as is well known in the art. A cam follower returnspring 60 is disposed in compression in a third well 62 in cam follower52 for biasing the cam follower into continuous contact with cam 56. InFIG. 2, cam follower 52 is in contact with a base circle portion 64 ofcam 56. A transverse bore 53 in shuttle 44 provides an oil flow pathbetween first and second check valves 40,42. Shuttle transverse bore 53further communicates with third well 62 via an axial passage 55 inshuttle 44.

Three-way valve 16 includes a valve body 66 mounted for convenience ontopump body 32. A first bore 68 is provided preferably coaxial withtransverse bore 34 in body 32 for flow of oil through body 66. Ofcourse, valve 16 may be mounted apart from pump 18 as desired andconnected thereto via an additional line. A spool 70, controllable as bya conventional solenoid or stepper motor or other means (none shown), isslidingly disposed in a second bore 72 in valve body 66. In a firstcontrol position, when oil pressure output from primary pump 14 isunacceptably low, spool 70 permits oil flow through pump 18, as shown inFIGS. 2 and 3. In a second control position, when oil pressure outputfrom primary pump 14 is acceptably high, spool 70 permits oil flow onlyfrom line 19 through orifices 70a and prevents oil flow through pump 18,as shown in FIG. 4.

The peristaltic pumping action of pump 18 is as follows. After initialfilling, shuttle transverse bore 53 between the check valves, passage55, and well 62 remain filled with oil at all times. When camshaft 58causes cam 56 to present a base circle portion 64 to follower 52, spring60 urges follower 52 away from the bottom of well 54, creating a space73 and thereby drawing oil from line 20 through check valve 42 to fillspace 73, the volume of which represents the per-stroke volume of thepump.

Referring to FIG. 3, when camshaft 58 rotates to cause cam 56 to presentan eccentric lobe 74 to follower 52, the follower is urged axially ofbore 54, overcoming return spring 60 (but not the stronger lost-motionspring 48), eliminating space 73, and expressing an equal volume of oilfrom shuttle transverse bore 53 through check valve 40 into line 21.Further rotation of camshaft 58 causes the follower to return to thenext base portion circle 64 of cam 56, refilling space 73 in preparationfor the next stroke of the pump.

Since the pump must respond continuously to the action of cam 56,whether or not oil is to be pumped into line 21, a lost motion mechanismmust be provided. Referring to FIG. 4, when valve 16 is closed to pump18, oil flow from the pump is deadheaded. Because oil is substantiallyincompressible, space 73 is not eliminated but rather follower 52 andshuttle 44 are displaced as a unit axially within blind bore 36 by adistance 71 equal to the height of space 73, overcoming lost-motionspring 48. Thus, when flow is shut off, shuttle 44 simply cycles withinpump body 32 to follow in lost motion the action of cam 56.

Cam 56 is shown in FIGS. 2-4 as having three base circle portionsegments 64 and three eccentric lobes 74. Thus one rotation of thecamshaft produces three strokes of the pump. Referring to FIGS. 5 and 6,an added advantage of a peristaltic secondary oil pump is shown. Curve76 represents the torque, both in the direction of camshaft rotation (+)and against the direction of camshaft rotation (−), exerted on camshaft58 in opening and closing three intake or exhaust valves of athree-cylinder engine, or one bank of a V-6 engine. Curve 78 representsthe torque exerted on camshaft 58 by one rotation of cam 56 in actuatingthe oil pump three times. By angularly orienting cam 56 on camshaft 58such that the pump-actuating lobes 74 are rotationally interspersedbetween the valve-actuating lobes 75, and preferably that each lobe 74is exactly 180° from one of the three valve cam lobes 75 (FIG. 6), thetorque resulting from the valve lobes and the pump lobes partiallycancel, the net camshaft torque oscillation being represented by curve80.

While the invention has been described by reference to various specificembodiments, it should be understood that numerous changes may be madewithin the spirit and scope of the inventive concepts described.Accordingly, it is intended that the invention not be limited to thedescribed embodiments, but will have full scope defined by the languageof the following claims.

What is claimed is:
 1. In an internal combustion engine having aperistaltic oil pump actuated by a cam on a camshaft of the engine, thepump-actuating cam having a plurality of pump-actuating lobes, thecamshaft being further provided with a plurality of additional camshaving individual lobes for actuating associated valves in the engine,the improvement wherein said pump-actuating lobes are spaced angularlyabout said pump-actuating cam and wherein said valve-opening lobes areangularly interspersed between said pump-actuating lobes.
 2. Animprovement in accordance with claim 1 wherein each of saidvalve-opening lobes is angularly equidistant from angularly adjacentpump-actuating lobes.
 3. A method for reducing the magnitude of torqueoscillation in a valve-actuating camshaft of an internal combustionengine, the camshaft supporting a plurality of valve-actuating cams,each valve-actuating cam having an individual lobe for actuating anengine valve and the valve-actuating lobes being angularly spaced aroundthe camshaft, comprising the steps of: a) providing a peristaltic oilpump actuated by a cam on said camshaft, said pump-actuating cam havinga plurality of pump-actuating lobes equal in number to the number ofvalve-actuating lobes and being angularly spaced around said camshaft;and b) orienting said pump-actuating cam on said camshaft such that saidpump-actuating lobes are angularly interspersed between saidvalve-actuating lobes.
 4. A method in accordance with claim 3 whereineach of said valve-actuating lobes is angularly equidistant fromangularly adjacent pump-actuating lobes.
 5. An internal combustionengine, comprising: a) a camshaft; b) a first cam disposed on saidcamshaft for actuating a peristaltic oil pump, said pump-actuating camhaving a plurality of pump-actuating lobes; c) a plurality of additionalcams disposed on said camshaft and having individual lobes for actuatingassociated valves in said engine, said additional cams being equal innumber to the number of pump-actuating lobes, wherein saidpump-actuating lobes are evenly spaced angularly about saidpump-actuating cam and wherein said valve-actuating lobes are angularlyinterspersed between said pump-actuating lobes, so that torque imposedon said camshaft by actuation of said valves is at least partiallyopposed by torque imposed by actuation of said pump, such that nettorque on said camshaft is diminished.
 6. An engine in accordance withclaim 5 wherein each of said valve-actuating lobes is angularlyequidistant from angularly adjacent pump-actuating lobes.